Various methods for extracorporeal blood treatment or cleaning are used to remove substances usually eliminated with urine and for fluid withdrawal. In hemodialysis, the patient's blood is cleaned outside the body in a dialyzer. The dialyzer comprises a blood chamber and a dialyzing fluid chamber, which are separated by a semipermeable membrane. During the treatment, the patient's blood flows through the blood chamber. In order to clean the blood effectively from substances usually eliminated with urine, fresh dialyzing fluid flows continuously through the dialyzing fluid chamber.
Whereas the transport of the lower-molecular weight substances through the membrane of the dialyzer is essentially determined by the concentration differences (diffusion) between the dialyzing fluid and the blood in the case of hemodialysis (HD), substances dissolved in the plasma water, in particular higher-molecular weight substances, are effectively removed by a high fluid flow (convection) through the membrane of the dialyzer in the case of hemofiltration (HF). In hemofiltration, the dialyzer functions as a filter. Hemodiafiltration (HDF) is a combination of the two processes.
In hemo(dia)filtration, part of the serum drawn off through the membrane of the dialyzer is replaced by a sterile substitution fluid, which is generally fed to the extracorporeal blood circuit either upstream of the dialyzer or downstream of the dialyzer. The supply of substitution fluid upstream of the dialyzer is also referred to as pre-dilution and the supply downstream of the dialyzer as post-dilution.
Apparatuses for hemo(dia)filtration are known, wherein the dialyzing fluid is prepared online from fresh water and dialyzing fluid concentrate and the substitution fluid is prepared online from the dialyzing fluid.
In the known hemo(dia)filtration apparatuses, the substitution fluid (substituate) is fed to the extracorporeal blood circuit from the fluid system of the machine via a substituate supply line. With pre-dilution, the substituate line leads to a connection point on the arterial blood line upstream of the dialyzer or filter, whereas with post-dilution the substituate line leads to a connection point on the venous blood line downstream of the dialyzer or filter. The substituate line comprises for example a connector with which it may be connected either to the venous or arterial blood line. In order to interrupt the fluid supply, a clamp or suchlike is provided on the substituate line. A hemo(dia)filtration apparatus of this kind is known for example from European Patent Publication No. EP 0 189 561.
The effectiveness of the blood treatment depends on whether the substitution fluid is fed to the extracorporeal blood circuit upstream or downstream of the dialyzer or filter. A knowledge of the mode of treatment, i.e., pre- or post-dilution, is therefore important.
European Patent Publication No. EP 1 348 458 A1 describes a method and a device for monitoring the supply of substitution fluid for an extracorporeal blood treatment apparatus. The propagation time of the pressure waves of a substituate pump disposed in the substituate line is measured in order to detect the supply of substitution fluid upstream or downstream of the dialyzer or filter. The supply of substituate upstream or downstream of the dialyzer or filter is detected on the basis of the propagation measurement. The known method requires the use of a substituate pump generating pressure waves.
There is known from German Patent Publication DE 10 2004 023 080 A1 a device for monitoring the supply of substitution fluid, wherein the supply of substituate upstream or downstream of the dialyzer or filter is detected on the basis of the change in the pressure, for example on the basis of a sudden pressure rise and/or pressure drop after the substituate pump is switched off or switched on. The known method requires the use of a substituate pump generating pressure waves.
A goal of example embodiments of the present invention is to provide a method for monitoring the supply of substitution fluid, which permits the detection of pre- or post-dilution with a high degree of reliability. Moreover, it is a goal of example embodiments of the present invention to provide a device for monitoring the supply of substitution fluid, with which the pre- and post-dilution may be reliably detected. A further goal of example embodiments of the present invention is to create an extracorporeal blood treatment apparatus with such a monitoring device.